Welding Inspector Duties and Responsibilities Section 1

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Main Responsibilities

1.1

Code compliance

Workmanship control Documentation control2 of 691

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Personal Attributes

1.1

Important qualities that good Inspectors are expected to have are:

Honesty

Integrity

Knowledge

Good communicator

Physical fitness

Good eyesight3 of 691

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Standard for Visual Inspection 1.1

Basic RequirementsBS EN 970 - Non-destructive examination of fusion welds - Visual examinationWelding Inspection Personnel should: be familiar with relevant standards, rules and specifications applicable to the fabrication work to be undertaken be informed about the welding procedures to be used have good vision (which should be checked every 12 months)

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Welding Inspection

1.2

Conditions for Visual Inspection (to BS EN 970) Illumination: 350 lux minimum required (recommends 500 lux - normal shop or office lighting)

Vision Access: eye should be within 600mm of the surface viewing angle (line from eye to surface) to be not less than 30600mm

30

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Welding InspectionWhen access is restricted may use: a mirrored boroscope a fibre optic viewing system

1.3

Aids to Visual Inspection (to BS EN 970)

}

Other aids: welding gauges (for checking bevel angles, weld profile, fillet sizing, undercut depth) dedicated weld-gap gauges and linear misalignment (high-low) gauges straight edges and measuring tapes magnifying lens (if magnification lens used it should have magnification between X2 to X5)

usually by agreement

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Welding Inspectors EquipmentMeasuring devices:

1.3

flexible tape, steel rule Temperature indicating crayons Welding gauges Voltmeter Ammeter Magnifying glass Torch / flash light Gas flow-meter

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Welding Inspectors Gauges10mm 10mm1 2

1.3

G.A.L.S.T.D. 16mm

G.A.L.

3 4

L

S.T.D. 16mm

5 6

Fillet Weld Gauges0 IN 1/4 1/2 3/4

TWI Multi-purpose Welding Gauge

Misalignment Gauges Hi-Lo Gauge8 of 691

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HI-LO Single Purpose Welding Gauge

Welding Inspectors Equipment

1.3

Voltmeter

Ammeter

Tong Tester4/23/2007 9 of 691

Welding Inspection 1.3Stages of Visual Inspection (to BS EN 970)Extent of examination and when required should be defined in the application standard or by agreement between the contracting parties For high integrity fabrications inspection required throughout the fabrication process:

Before welding (Before assemble & After assembly) During welding After welding

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Typical Duties of a Welding InspectorBefore WeldingPreparation:

1.5

Familiarisation with relevant documents Application Standard/Code - for visual acceptance requirements

Drawings - item details and positions/tolerances etcQuality Control Procedures - for activities such as material handling, documentation control, storage & issue of welding consumables Quality Plan/Inspection & Test Plan/Inspection Checklist details of inspection requirements, inspection procedures & records required11 of 691

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Typical Duties of a Welding InspectorBefore WeldingWelding Procedures:

1.5

are applicable to joints to be welded & approvedare available to welders & inspectors

Welder Qualifications:

list of available qualified welders related to WPSscertificates are valid and in-date

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Typical Duties of a Welding Inspector 1.5Before WeldingEquipment: all inspection equipment is in good condition & calibrated as necessary all safety requirements are understood & necessary equipment available Materials: can be identified & related to test certificates, traceability ! are of correct dimensions are in suitable condition (no damage/contamination)

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Typical Duties of a Welding Inspector 1.5Before WeldingConsumables: in accordance with WPSs are being controlled in accordance with Procedure Weld Preparations: comply with WPS/drawing

free from defects & contaminationWelding Equipment: in good order & calibrated as required by Procedure

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Typical Duties of a Welding Inspector 1.5Before WeldingFit-up

complies with WPS Number / size of tack welds to Code / good workmanship

Pre-heat if specified

minimum temperature complies with WPS

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Typical Duties of a Welding InspectorDuring WeldingWeather conditions

1.5

suitable if site / field welding

Welding Process(es) in accordance with WPS

Welder is approved to weld the joint

Pre-heat (if required) minimum temperature as specified by WPS maximum interpass temperature as WPS

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Typical Duties of a Welding InspectorDuring WeldingWelding consumables in accordance with WPS in suitable condition controlled issue and handling Welding Parameters current, voltage & travel speed as WPS Root runs if possible, visually inspect root before single-sided welds are filled up

1.6

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Typical Duties of a Welding InspectorDuring WeldingInter-run cleaning in accordance with an approved method (& back gouging) to good workmanship standard Distortion control welding is balanced & over-welding is avoided

1.6

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Typical Duties of a Welding InspectorAfter WeldingWeld Identification identified/numbered as required is marked with welders identity

1.6

Visual Inspection ensure weld is suitable for all NDT visually inspect & sentence to Code requirements

Dimensional Survey ensure dimensions comply with Code/drawing

Other NDT ensure all NDT is completed & reports available19 of 691

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Typical Duties of a Welding InspectorAfter WeldingRepairs

1.6

monitor repairs to ensure compliance with Procedure, ensure NDT after repairs is completed PWHT monitor for compliance with Procedure check chart records confirm Procedure compliance Pressure / Load Test ensure test equipment is suitably calibrated monitor to ensure compliance with Procedure ensure all records are available

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Typical Duties of a Welding InspectorAfter WeldingDocumentation ensure any modifications are on as-built drawings ensure all required documents are available Collate / file documents for manufacturing records Sign all documentation and forward it to QC department.

1.6

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Summary of DutiesIt is the duty of a Welding Inspector to ensure all the welding and associated actions are carried out in accordance with the specification and any applicable procedures.

A Welding Inspector must: Observe To observe all relevant actions related to weld quality throughout production. Record To record, or log all production inspection points relevant to quality, including a final report showing all identified imperfections

Compare To compare all recorded information with the acceptance criteria and any other relevant clauses in the applied application standard

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Welding InspectorTerms & Definitions Section 2

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Welding Terminology & DefinitionsWhat is a Weld?

2.1

A localised coalescence of metals or non-metals produced either by heating the materials to the welding temperature, with or without the application of pressure, or by the application of pressure alone (AWS) A permanent union between materials caused by heat, and or pressure (BS499) An Autogenous weld: A weld made with out the use of a filler material and can only be made by TIG or Oxy-Gas Welding

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Welding Terminology & DefinitionsWhat is a Joint?

2.1

The junction of members or the edges of members that are to be joined or have been joined (AWS) A configuration of members (BS499)

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Joint Terminology 2.2

Edge

Open & Closed Corner

Lap

Cruciform4/23/2007

Tee

Butt26 of 691

Welded Butt Joints 2.2Butt A_________Welded butt joint

Fillet A_________Welded butt joint

Compound A____________Welded butt joint

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Welded Tee Joints 2.2

Fillet A_________Welded T joint

Butt A_________Welded T joint

Compound A____________Welded T joint

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Weld Terminology 2.3

Butt weld

Fillet weld

Spot weld

Edge weld

Plug weld Compound weld

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Butt Preparations Sizes

2.4

Partial Penetration Butt WeldActual Throat Thickness Design Throat Thickness

Full Penetration Butt WeldActual Throat Thickness

Design Throat Thickness

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Weld Zone Terminology 2.5AFace

B

Weld metalHeat Affected Zone Weld Boundary

CRoot

D

A, B, C & D = Weld Toes4/23/2007 31 of 691

Weld Zone Terminology 2.5Weld cap width

Excess Cap height or Weld Reinforcement

Actual Throat Thickness

Design Throat Thickness

Excess Root Penetration4/23/2007 32 of 691

Heat Affected Zone (HAZ) 2.5Maximum Temperature solid weld metal solid-liquid Boundary grain growth zone recrystallised zone partially transformed zone tempered zone unaffected base material

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Joint Preparation Terminology 2.7Included angleAngle of bevel Root Radius

Included angle

Root Face Root Gap Root Gap

Root Face

Single-V Butt4/23/2007

Single-U Butt34 of 691

Joint Preparation TerminologyAngle of bevel

2.8 & 2.9

Angle of bevel

Root Radius

Root Face

Root Gap

Root Gap

Root Face

Land

Single Bevel Butt4/23/2007

Single-J Butt35 of 691

Single Sided Butt Preparations

2.10

Single sided preparations are normally made on thinner materials, or when access form both sides is restricted

Single Bevel

Single Vee

Single-J4/23/2007

Single-U36 of 691

Double Sided Butt Preparations

2.11

Double sided preparations are normally made on thicker materials, or when access form both sides is unrestricted

Double -Bevel

Double -Vee

Double - J4/23/2007

Double - U37 of 691

Weld PreparationTerminology & Typical Dimensions:bevel angle included angle

V-Joints

root face root gap

Typical Dimensions bevel angle root face root gap 30 to 35 ~1.5 to ~2.5mm ~2 to ~4mm

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Butt Weld - Toe Blend6 mm

Most codes quote the weld toes shall blend smoothly

80

Poor Weld Toe Blend Angle3 mm

This statement is not quantitative and therefore open to individual interpretationThe higher the toe blend angle the greater the amount of stress concentration The toe blend angle ideally should be between 20o-30o

20

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Fillet Weld Features

2.13

Excess Weld Metal

Vertical Leg Length

Design Throat

Horizontal leg Length

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Fillet Weld Throat Thickness

2.13

aa = Design Throat Thickness b = Actual Throat Thickness

b

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Deep Penetration Fillet Weld Features 2.13

aa = Design Throat Thickness b = Actual Throat Thickness

b

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Fillet Weld Sizes

2.14

Calculating Throat Thickness from a known Leg Length: Design Throat Thickness = Leg Length x 0.7 Question: The Leg length is 14mm.

What is the Design Throat?Answer: 14mm x 0.7 = 10mm Throat Thickness

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Fillet Weld Sizes

2.14

Calculating Leg Length from a known Design Throat Thickness:

Leg Length = Design Throat Thickness x 1.4Question: The Design Throat is 10mm. What is the Leg length? Answer: 10mm x 1.4 = 14mm Leg Length

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Features to Consider 2

2.14

Importance of Fillet Weld Leg Length Size(a) (b)

4mm 4mm

8mm 2mm

Approximately the same weld volume in both Fillet Welds, but the effective throat thickness has been altered, reducing considerably the strength of weld B4/23/2007 45 of 691

Fillet Weld Sizes(a)Excess

2.14

Importance of Fillet weld leg length Size(b) 6mm (a) 4mm (b) 6mmExcess

4mm

Area = 4 x 4 = 8mm2 2

Area = 6 x 6 = 18mm2 2

The c.s.a. of (b) is over double the area of (a) without the extra excess weld metal being added4/23/2007 46 of 691

Fillet Weld ProfilesFillet welds - Shape

2.15

Mitre Fillet

Convex FilletA concave profile is preferred for joints subjected to fatigue loading

Concave Fillet4/23/2007

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Fillet Features to ConsiderEFFECTIVE THROAT THICKNESSa = Nominal throat thickness

2.15

s = Effective throat thickness

a

s

Deep penetration fillet welds from high heat input welding process MAG, FCAW & SAW etc4/23/2007 48 of 691

Welding PositionsPA PB PC PD PE PF PG H-L045 J-L0454/23/2007

2.17

1G / 1F 2F 2G 4F 4G 3G / 5G 3G / 5G 6G 6G

Flat / Downhand Horizontal-Vertical Horizontal Horizontal-Vertical (Overhead) Overhead Vertical-Up Vertical-Down Inclined Pipe (Upwards) Inclined Pipe (Downwards)49 of 691

Welding Positions

2.17

ISO

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Welding position designation 2.17Butt welds in plate (see ISO 6947)

Flat - PA Vertical up - PF

Overhead - PE

Vertical down - PG4/23/2007

Horizontal - PC51 of 691

Welding position designation 2.17Butt welds in pipe (see ISO 6947)

Flat - PAaxis: horizontal pipe: rotated

Vertical up - PF Vertical down - PGaxis: horizontal pipe: fixed axis: horizontal pipe: fixed

H-L0454/23/2007

J-L045

Horizontal - PC52 of 691

axis: inclined at 45 axis: inclined at 45 axis: vertical pipe: fixed pipe: fixed pipe: fixed

Welding position designation 2.17Fillet welds on plate (see ISO 6947)

Flat - PA

Horizontal - PB

Overhead - PD

Vertical up - PF4/23/2007

Vertical down - PG53 of 691

Welding position designation 2.17Fillet welds on pipe (see ISO 6947)

Flat - PAaxis: inclined at 45 pipe: rotated

Horizontal - PBaxis: vertical pipe: fixed

Overhead - PDaxis: vertical pipe: fixed

Horizontal - PB Vertical up - PF Vertical down - PGaxis: horizontal pipe: rotated4/23/2007

axis: horizontal pipe: fixed

axis: horizontal pipe: fixed54 of 691

Plate/Fillet Weld Positions

2.17

PA / 1G

PA / 1F PF / 3G

PB / 2F

PC / 2G

PD / 4F4/23/2007

PE / 4G

PG / 3G55 of 691

Pipe Welding Positions

2.17

PA / 1GWeld: Flat Pipe: rotated Axis: Horizontal

PF / 5GWeld: Vertical upwards Pipe: Fixed Axis: Horizontal 45o

PG / 5GWeld: Vertical Downwards Pipe: Fixed Axis: Horizontal 45o

PC / 2GWeld: Horizontal Pipe: Fixed Axis: Vertical4/23/2007

H-LO 45 / 6GWeld: Upwards Pipe: Fixed Axis: Inclined

J-LO 45 / 6GWeld: Downwards Pipe: Fixed Axis: Inclined56 of 691

Travel Speed Measurement

2.18

Definition: the rate of weld progression measured in case of mechanised and automatic welding processes in case of MMA can be determined using ROL and arc time

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Welding InspectorWelding Imperfections Section 3

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Welding ImperfectionsAll welds have imperfections

3.1

Imperfections are classed as defects when they are of a type, or size, not allowed by the Acceptance Standard

A defect is an unacceptable imperfection A weld imperfection may be allowed by one Acceptance Standard but be classed as a defect by another Standard and require removal/rectification

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Welding ImperfectionsStandards for Welding Imperfections

3.1

BS EN ISO 6520-1(1998) Welding and allied processes Classification of geometric imperfections in metallic materials Part 1: Fusion welding Imperfections are classified into 6 groups, namely: 1 Cracks 2 Cavities 3 Solid inclusions 4 Lack of fusion and penetration 5 Imperfect shape and dimensions 6 Miscellaneous imperfections

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Welding ImperfectionsStandards for Welding Imperfections

3.1

EN ISO 5817 (2003) Welding - Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) - Quality levels for imperfections This main imperfections given in EN ISO 6520-1 are listed in EN ISO 5817 with acceptance criteria at 3 levels, namely

Level B (highest)Level C (intermediate) Level D (general) This Standard is directly applicable to visual testing of welds ...(weld surfaces & macro examination)

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Welding imperfections classification

3.1

Cracks

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Cracks

3.1

Cracks that may occur in welded materials are caused generally by many factors and may be classified by shape and position.Classified by Shape Longitudinal Transverse Chevron Lamellar Tear Classified by Position HAZ Centerline Crater Fusion zone Parent metal

Note: Cracks are classed as Planar Defects.4/23/2007 63 of 691

Cracks

3.1

Longitudinal parent metal

Transverse weld metal

Longitudinal weld metal Lamellar tearing4/23/2007 64 of 691

Cracks

3.1

Transverse crack4/23/2007

Longitudinal crack65 of 691

Cracks

3.2

Main Crack Types Solidification Cracks Hydrogen Induced Cracks Lamellar Tearing Reheat cracks

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CracksSolidification Cracking

3.2

Occurs during weld solidification process

Steels with high sulphur impurities content (low ductility at elevated temperature) Requires high tensile stress

Occur longitudinally down centre of weld

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Cracks

3.3

Hydrogen Induced Cold Cracking Requires susceptible hard grain structure, stress, low temperature and hydrogen Hydrogen enters weld via welding arc mainly as result of contaminated electrode or preparation

Hydrogen diffuses out into parent metal on cooling Cracking developing most likely in HAZ

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Lamellar Tearing Location: Parent metal

3.5

Steel Type: Any steel type possible Susceptible Microstructure: Poor through thickness ductility

Lamellar tearing has a step like appearance due to the solid inclusions in the parent material (e.g. sulphides and silicates) linking up under the influence of welding stresses Low ductile materials in the short transverse direction containing high levels of impurities are very susceptible to lamellar tearing It forms when the welding stresses act in the short transverse direction of the material (through thickness direction)69 of 691

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Gas CavitiesGas pore Cluster porosity

3.6

Causes: Loss of gas shield Damp electrodes Contamination

Blow hole Herringbone porosity

Arc length too large Damaged electrode flux Moisture on parent material Welding current too low Gas pore 1.6mm

Root piping

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Gas Cavities

3.7

Porosity

Root piping

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Gas Cavities

3.8

Cluster porosity4/23/2007

Herringbone porosity72 of 691

Crater Pipe

3.9

Weld crater

Crater pipe

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Crater Pipe

3.9

Crater pipe is a shrinkage defect and not a gas defect, it has the appearance of a gas pore in the weld crater

Crater cracks (Star cracks)

Causes:

Too fast a cooling rate Deoxidization reactions and liquid to solid volume change Contamination74 of 691

Crater pipe

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Solid Inclusions

3.10

Slag inclusions are defined as a non-metallic inclusion caused by some welding processCauses: Slag originates from welding fluxSlag inclusions Lack of sidewall fusion with associated slag

MAG and TIG welding process produce silica inclusions Slag is caused by inadequate cleaning

Parallel slag lines

Lack of interun fusion + slag

Other inclusions include tungsten and copper inclusions from the TIG and MAG welding process75 of 691

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Solid Inclusions

3.11

Interpass slag inclusions

Elongated slag lines

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Welding ImperfectionsTypical Causes of Lack of Fusion: welding current too low

3.13

bevel angle too steep root face too large (single-sided weld) root gap too small (single-sided weld) incorrect electrode angle linear misalignment welding speed too high welding process related particularly dip-transfer GMAW flooding the joint with too much weld metal (blocking Out)

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Lack of FusionCauses:

3.13

Poor welder skill Incomplete filled groove + Lack of sidewall fusion

Incorrect electrode manipulation Arc blow

1 2 1. Lack of sidewall fusion 2. Lack of inter-run fusion

Incorrect welding current/voltage Incorrect travel speed Incorrect inter-run cleaning

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Lack of Fusion

3.13

Lack of sidewall fusion + incomplete filled groove4/23/2007 79 of 691

Weld Root Imperfections

3.15

Lack of Root Fusion

Lack of Root Penetration80 of 691

4/23/2007

Cap Undercut

3.18

Intermittent Cap Undercut4/23/2007 81 of 691

Undercut

3.18

Root undercut4/23/2007

Cap undercut82 of 691

Surface and Profile

3.19

Incomplete filled groovePoor cap profiles and excessive cap reinforcements may lead to stress concentration points at the weld toes and will also contribute to overall poor toe blend

Poor cap profile

Excessive cap height83 of 691

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Surface and Profile

3.19

Excess cap reinforcement4/23/2007

Incomplete filled groove84 of 691

Weld Root Imperfections

3.20

Excessive root penetration4/23/2007 85 of 691

Overlap

3.21

An imperfection at the toe or root of a weld caused by metal flowing on to the surface of the parent metal without fusing to it

Causes: Contamination Slow travel speed Incorrect welding technique

Current too low

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OverlapToe Overlap

3.21

Toe Overlap

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Set-Up Irregularities

3.22

Linear misalignment is measured from the lowest plate to the highest point. Plate/pipe Linear Misalignment (Hi-Lo) Angular misalignment is measured in degrees

Angular Misalignment

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Set-Up Irregularities

3.22

Linear Misalignment4/23/2007 89 of 691

Set-Up Irregularities

3.22

Linear Misalignment

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Incomplete Groove

3.23

Lack of sidewall fusion + incomplete filled groove4/23/2007 91 of 691

Weld Root ImperfectionsCauses:

3.24

A shallow groove, which may occur in the root of a butt weld

Excessive back purge

pressure during TIG welding

Concave Root

Excessive root bead grinding before the application of the second passwelding current too high for 2nd pass overhead welding root gap too large - excessive weaving

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Weld Root Imperfections

3.24

Concave Root

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Weld Root Imperfections

3.24

Concave root4/23/2007

Excess root penetration94 of 691

Weld Root ImperfectionsA localized collapse of the weld pool due to excessive penetration resulting in a hole in the root run

3.25

Causes:

High Amps/volts Small Root face Large Root Gap Slow Travel Speed

Burn through

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Weld Root Imperfections

3.25

Burn Through

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Oxidized Root (Root Coking)Causes:

Loss or insufficient back purging gas (TIG)

Most commonly occurswhen welding stainless steels

Purging gases include argon, helium and

occasionally nitrogen4/23/2007 97 of 691

Miscellaneous ImperfectionsCauses:

3.26

Accidental striking of the arc onto the parent material Faulty electrode holder

Poor cable insulation Poor return lead clamping

Arc strike4/23/2007 98 of 691

Miscellaneous ImperfectionsCauses:

3.27

Excessive current Damp electrodes Contamination

Incorrect wire feed speed when welding with the MAG welding processArc blow99 of 691

Spatter4/23/2007

Mechanical Damage

3.28

Mechanical damage can be defined as any surface material damage cause during the manufacturing process. Grinding Hammering Chiselling Chipping Breaking off welded attachments (torn surfaces) Using needle guns to compress weld capping runs4/23/2007 100 of 691

Mechanical DamageChipping Marks

3.28

Mechanical Damage/Grinding Mark4/23/2007 101 of 691

Welding InspectorDestructive Testing Section 4

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Qualitative and Quantitative Tests 4.1The following mechanical tests have units and are termed quantitative tests to measure Mechanical Properties Tensile tests (Transverse Welded Joint, All Weld Metal) Toughness testing (Charpy, Izod, CTOD) Hardness tests (Brinell, Rockwell, Vickers)

The following mechanical tests have no units and are termed qualitative tests for assessing joint quality Macro testing Bend testing Fillet weld fracture testing Butt weld nick-break testing4/23/2007 104 of 691

Mechanical Test Samples 4.1Tensile SpecimensCTOD Specimen

Bend Test Specimen Charpy Specimen Fracture Fillet Specimen

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Destructive Testing 4.1WELDING PROCEDURE QUALIFICATION TESTING top of fixed pipe 2 Typical Positions for Test Pieces Specimen Type Macro + Hardness 3 Transverse Tensile Position 5 2, 4

Bend TestsCharpy Impact Tests 4 54/23/2007

2, 43 3

Additional Tests

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DefinitionsMechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

Malleability Ductility Toughness Hardness

Ability of a material to withstand deformation under static compressive loading without rupture

Tensile Strength

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DefinitionsMechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

Malleability Ductility Toughness Hardness

Tensile Strength

Ability of a material undergo plastic deformation under static tensile loading without rupture. Measurable elongation and reduction in cross section area

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DefinitionsMechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

Malleability Ductility Toughness Hardness

Ability of a material to withstand bending or the application of shear stresses by impact loading without fracture.

Tensile Strength

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DefinitionsMechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

Malleability Ductility Toughness Hardness Tensile Strength

Measurement of a materials surface resistance to indentation from another material by static load

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DefinitionsMechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.

Malleability Ductility Toughness Hardness Tensile Strength

Measurement of the maximum force required to fracture a materials bar of unit cross-sectional area in tension

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Transverse Joint Tensile Test

4.2

Weld on plate

Weld on pipe4/23/2007

Multiple cross joint specimens112 of 691

Tensile Test

4.3

All-Weld Metal Tensile Specimen

Transverse Tensile Specimen

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STRA (Short Transverse Reduction Area)For materials that may be subject to Lamellar Tearing

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UTS Tensile test

4.4

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Charpy V-Notch Impact Test 4.5

Objectives: measuring impact strength in different weld joint areas assessing resistance toward brittle fracture Information to be supplied on the test report: Material type Notch type Specimen size Test temperature Notch location Impact Strength Value

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Ductile / Brittle Transition CurveTemperature range

4.6

Ductile fracture 47 Joules

Transition range

Ductile/Brittle transition point 28 Joules Energy absorbed

Brittle fracture - 50 - 40 - 30 - 20 - 10 0 Testing temperature - Degrees Centigrade Three specimens are normally tested at each temperature4/23/2007 117 of 691

Comparison Charpy Impact Test Results 4.6Impact Energy JoulesRoom Temperature 1. 2. 3. 197 Joules 191 Joules 186 Joules -20oC Temperature 1. 2. 3. 49 Joules 53 Joules 51 Joules

Average = 191 Joules

Average = 51 Joules

The test results show the specimens carried out at room temperature absorb more energy than the specimens carried out at -20oC4/23/2007 118 of 691

Charpy V-notch impact test specimen 4.7Specimen dimensions according ASTM E23

ASTM: American Society of Testing Materials4/23/2007 119 of 691

Charpy V-Notch Impact Test 4.8Specime n Pendulu m (striker)

Anvil (support)4/23/2007 120 of 691

Charpy Impact Test22.5o 2 mm 10 mm

4.9

100% BrittleMachined notchFracture surface 100% bright crystalline brittle fracture

8 mm

100% DuctileMachined notch Large reduction in area, shear lips

Randomly torn, dull gray fracture surface4/23/2007 121 of 691

Hardness TestingDefinition

4.10

Measurement of resistance of a material against penetration of an indenter under a constant load There is a direct correlation between UTS and hardness

Hardness tests:Brinell Vickers Rockwell4/23/2007 122 of 691

Hardness TestingObjectives:

4.10

measuring hardness in different areas of a welded joint assessing resistance toward brittle fracture, cold cracking and corrosion sensitivity within a H2S (Hydrogen Sulphide) environment.

Information to be supplied on the test report: material type location of indentation type of hardness test and load applied on the indenter hardness value

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Vickers Hardness TestVickers hardness tests:

4.11

indentation body is a square based diamond pyramid (136 included angle)the average diagonal (d) of the impression is converted to a hardness number from a table it is measured in HV5, HV10 or HV025Diamond indentor Indentation Adjustable shutters

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Vickers Hardness Test Machine

4.11

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Brinell Hardness Test

4.11

Hardened steel ball of given diameter is subjected for

a given time to a given load Load divided by area of indentation gives Brinell hardness in kg/mm2 More suitable for on site hardness testing 30KN

=10mm steel ball4/23/2007 126 of 691

Rockwell Hardness TestRockwell B1KN 1.5KN

Rockwell C

=1.6mm steel ball

120 Diamond Cone

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Hardness Testingusually the hardest region fusion line or fusion boundary

4.12

1.5 to 3mm

HAZ

Hardness Test Methods Vickers Rockwell Brinell

Typical Designations 240 HV10 Rc 22 200 BHN-W

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Crack Tip Opening Displacement testing 4.12 Test is for fracture toughness Square bar machined with a notch placed in the centre. Tested below ambient temperature at a specified temperature. Load is applied at either end of the test specimen in an attempt to open a crack at the bottom of the notch Normally 3 samples4/23/2007 129 of 691

Fatigue Fracture

4.13

Location: Any stress concentration area

Steel Type: All steel typesSusceptible Microstructure: All grain structures Test for Fracture Toughness is CTOD (Crack Tip Opening Displacement)

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Fatigue Fracture

4.13

Fatigue cracks occur under cyclic stress conditions

Fracture normally occurs at a change in section, notch and weld defects i.e stress concentration areaAll materials are susceptible to fatigue cracking

Fatigue cracking starts at a specific point referred to as a initiation pointThe fracture surface is smooth in appearance sometimes displaying beach markings The final mode of failure may be brittle or ductile or a combination of both131 of 691

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Fatigue FracturePrecautions against Fatigue Cracks

Toe grinding, profile grinding.The elimination of poor profiles The elimination of partial penetration welds and weld defects Operating conditions under the materials endurance limits

The elimination of notch effects e.g. mechanical damage cap/root undercutThe selection of the correct material for the service conditions of the component132 of 691

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Fatigue FractureFatigue fracture occurs in structures subject to repeated application of tensile stress. Crack growth is slow (in same cases, crack may grow into an area of low stress and stop without failure).

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Fatigue FractureSecondary mode of failure ductile fracture rough fibrous appearance Fatigue fracture surface smooth in appearance

Initiation points / weld defects4/23/2007 134 of 691

Fatigue FractureFatigue fracture distinguish features: Crack growth is slow

It initiate from stress concentration points load is considerably below the design or yield stress level The surface is smooth The surface is bounded by a curve Bands may sometimes be seen on the smooth surface beachmarks. They show the progress of the crack front from the point of origin The surface is 90 to the load

Final fracture will usually take the form of gross yielding (as the maximum stress in the remaining ligament increase!) Fatigue crack need initiation + propagation periods

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Bend TestsObject of test:

4.15

To determine the soundness of the weld zone. Bend testing can also be used to give an assessment of weld zone ductility. There are three ways to perform a bend test:

Face bend Root bend Side bend

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Bending test

4.16

Types of bend test for welds (acc. BS EN 910):

t up to 12 mm

Root / face bend

Thickness of material - t t over 12 mm

Side bend

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Fillet Weld Fracture TestsObject of test:

4.17

To break open the joint through the weld to permit examination of the fracture surfaces Specimens are cut to the required length A saw cut approximately 2mm in depth is applied along the fillet welds length Fracture is usually made by striking the specimen with a single hammer blow Visual inspection for defects

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Fillet Weld Fracture TestsHammer

4.17

2mm Notch

Fracture should break weld saw cut to root4/23/2007 139 of 691

Fillet Weld Fracture Tests

4.17

This fracture indicates lack of fusion

This fracture has occurred saw cut to root

Lack of Penetration4/23/2007 140 of 691

Nick-Break TestObject of test:

4.18

To permit evaluation of any weld defects across the fracture surface of a butt weld. Specimens are cut transverse to the weld A saw cut approximately 2mm in depth is applied along the welds root and cap Fracture is usually made by striking the specimen with a single hammer blow

Visual inspection for defects

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Nick-Break TestNotch cut by hacksaw

4.18

2 mm 19 mm 2 mm

Approximately 230 mm

Weld reinforcement may or may not be removed

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Nick Break Test

4.18

Alternative nick-break test specimen, notch applied all way around the specimen

Lack of root penetration or fusion

Inclusions on fracture line

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Summary of Mechanical Testing 4.19We test welds to establish minimum levels of mechanical properties, and soundness of the welded joint We divide tests into Qualitative & Quantitative methods:

Quantitative: (Have units/numbers) To measure mechanical properties Hardness (VPN & BHN)

Qualitative: (Have no units/numbers) For assessing joint quality Macro tests

Toughness (Joules & ft.lbs)Strength (N/mm2 & PSI, MPa) Ductility / Elongation (E%)

Bend testsFillet weld fracture tests Butt Nick break tests

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Welding InspectorWPS Welder Qualifications Section 5

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Welding Procedure Qualification 5.1Question: What is the main reason for carrying out a Welding Procedure Qualification Test ? (What is the test trying to show ?) Answer: To show that the welded joint has the properties* that satisfy the design requirements (fit for purpose)

* properties mechanical properties are the main interest - always strength but toughness & hardness may be important for some applications test also demonstrates that the weld can be made without defects

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Welding ProceduresProducing a welding procedure involves: Planning the tasks

5.1

Collecting the data Writing a procedure for use of for trial Making a test welds Evaluating the results Approving the procedure

Preparing the documentation

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Welding Procedures 5.2In most codes reference is made to how the procedure are to be devised and whether approval of these procedures is required. The approach used for procedure approval depends on the code: Example codes: AWS D.1.1: Structural Steel Welding Code BS 2633: Class 1 welding of Steel Pipe Work API 1104: Welding of Pipelines BS 4515: Welding of Pipelines over 7 Bar

Other codes may not specifically deal with the requirement of a procedure but may contain information that may be used in writing a weld procedure 4/23/2007

EN 1011Process of Arc Welding Steels148 of 691

Welding Procedure Qualification 5.3(according to EN ISO 15614)

The welding engineer writes qualified Welding Procedure Specifications (WPS) for production welding

Production welding conditions must remain within the range of qualification allowed by the WPQR

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Welding Procedure Qualification(according to EN Standards)

5.3

welding conditions are called welding variables welding variables are classified by the EN ISO Standard as:

Essential variablesNon-essential variables Additional variablesNote: additional variables = ASME supplementary essential The range of qualification for production welding is based on the limits that the EN ISO Standard specifies for essential variables* (* and when applicable - the additional variables)4/23/2007 150 of 691

Welding Procedure Qualification(according to EN Standards)

5.3

WELDING ESSENTIAL VARIABLESQuestion:

Why are some welding variables classified as essential ?Answer: A variable, that if changed beyond certain limits (specified by the Welding Standard) may have a significant effect on the properties* of the joint * particularly joint strength and ductility

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Welding Procedure Qualification 5.3(according to EN Standards)

SOME TYPICAL ESSENTIAL VARIABLES Welding Process

Post Weld Heat Treatment (PWHT) Material Type Electrode Type, Filler Wire Type (Classification) Material Thickness Polarity (AC, DC+ve / DC-ve) Pre-Heat Temperature Heat Input

Welding Position

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Welding Procedures Type (Grouping) Thickness Diameter (Pipes) Surface condition)

5.3

Components of a welding procedure Parent material

Welding process Type of process (MMA, MAG, TIG, SAW etc) Equipment parameters Amps, Volts, Travel speed

Welding Consumables Type of consumable/diameter of consumable Brand/classification Heat treatments/ storage4/23/2007 153 of 691

Welding ProceduresJoint designEdge preparation Root gap, root face Jigging and tacking Type of baking

5.3

Components of a welding procedure

Welding PositionLocation, shop or site Welding position e.g. 1G, 2G, 3G etc Any weather precaution

Thermal heat treatmentsPreheat, temps Post weld heat treatments e.g. stress relieving4/23/2007 154 of 691

Welding ProceduresObject of a welding procedure test

5.3

To give maximum confidence that the welds mechanical and metallurgical properties meet the requirements of the applicable code/specification. Each welding procedure will show a range to which the procedure is approved (extent of approval) If a customer queries the approval evidence can be supplied to prove its validity

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Welding ProceduresSummary of designations: pWPS: Preliminary Welding Procedure Specification(Before procedure approval)

WPAR (WPQR): Welding Procedure Approval Record(Welding procedure Qualification record)

WPS: Welding Procedure Specification(After procedure approval)

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Example:

WeldingProcedure Specification (WPS)

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Welder Qualification

5.4

Numerous codes and standards deal with welder qualification, e.g. BS EN 287. Once the content of the procedure is approved the next stage is to approve the welders to the approved procedure. A welders test know as a Welders Qualification Test (WQT). Object of a welding qualification test: To give maximum confidence that the welder meets the quality requirements of the approved procedure (WPS). The test weld should be carried out on the same material and same conditions as for the production welds.

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Welder Qualification(according to EN Standards) Question: What is the main reason for qualifying a welder ?

5.4 & 5.5

Answer: To show that he has the skill to be able to make production welds that are free from defects Note: when welding in accordance with a Qualified WPS

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Welder Qualification (according to EN 287 )

5.5

The welder is allowed to make production welds within the range of qualification shown on the Certificate The range of qualification allowed for production welding is based on the limits that the EN Standard specifies for the welder qualification essential variables A Certificate may be withdrawn by the Employer if there is reason to doubt the ability of the welder, for example a high repair rate not working in accordance with a qualified WPS

The qualification shall remain valid for 2 years provided there is certified confirmation of welding to the WPS in that time. A Welders Qualification Certificate automatically expires if the welder has not used the welding process for 6 months or longer.4/23/2007 160 of 691

Welding Procedure Qualification 5.7(according to EN ISO 15614) Welding Engineer writes a preliminary Welding Procedure Specification (pWPS) for each test weld to be made

A welder makes a test weld in accordance with the pWPS A welding inspector records all the welding conditions used for the test weld (referred to as the as-run conditions) An Independent Examiner/ Examining Body/ Third Party inspector may be requested to monitor the qualification process The finished test weld is subjected to NDT in accordance with the methods specified by the EN ISO Standard - Visual, MT or PT & RT or UT4/23/2007 161 of 691

Welding Procedure Qualification 5.7(according to EN ISO 15614) Test weld is subjected to destructive testing (tensile, bend, macro) The Application Standard, or Client, may require additional tests such as impact tests, hardness tests (and for some materials - corrosion tests)

A Welding Procedure Qualification Record (WPQR) is prepared giving details of: The welding conditions used for the test weld Results of the NDT Results of the destructive tests The welding conditions that the test weld allows for production welding The Third Party may be requested to sign the WPQR as a true record4/23/2007 162 of 691

Welder Qualification(according to EN 287 )

5.9

An approved WPS should be available covering the range of qualification required for the welder approval. The welder qualifies in accordance with an approved WPS

A welding inspector monitors the welding to make sure that the welder uses the conditions specified by the WPSEN Welding Standard states that an Independent Examiner, Examining Body or Third Party Inspector may be required to monitor the qualification process

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Welder Qualification(according to EN 287 )

5.9

The finished test weld is subjected to NDT by the methods specified by the EN Standard - Visual, MT or PT & RT or UT The test weld may need to be destructively tested - for certain materials and/or welding processes specified by the EN Standard or the Client Specification A Welders Qualification Certificate is prepared showing the conditions used for the test weld and the range of qualification allowed by the EN Standard for production welding The Qualification Certificate is usually endorsed by a Third Party Inspector as a true record of the test

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Welder Qualification Welders name and identification number Date of test and expiry date of certificate Standard/code e.g. BS EN 287 Test piece details Welding process. Welding parameters, amps, volts Consumables, flux type and filler classification details Sketch of run sequence Welding positions Joint configuration details Material type qualified, pipe diameter etc Test results, remarks Test location and witnessed by Extent (range) of approval4/23/2007

5.10

Information that should be included on a welders test certificate are, which the welder should have or have access to a copy of !

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Welding InspectorMaterials Inspection Section 6

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Material InspectionOne of the most important items to consider is Traceability. The materials are of little use if we can not, by use of an effective QA system trace them from specification and purchase order to final documentation package handed over to the Client. All materials arriving on site should be inspected for: Size / dimensions

Condition Type / specification In addition other elements may need to be considered depending on the materials form or shape

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Pipe Inspection(Corrosion, Damage, Wall thickness Ovality, Laminations & Seam)

We inspect the condition

Specification

LP5

Welded seam

Size

Other checks may need to be made such as: distortion tolerance, number of plates and storage.4/23/2007 169 of 691

Plate InspectionWe inspect the condition (Corrosion, Mechanical damage, Laps, Bands & Laminations) Specification5L

Size

Other checks may need to be made such as: distortion tolerance, number of plates and storage.4/23/2007 170 of 691

Parent Material ImperfectionsMechanical damage Lap

Lamination

Segregation line Laminations are caused in the parent plate by the steel making process, originating from ingot casting defects. Segregation bands occur in the centre of the plate and are low melting point impurities such as sulphur and phosphorous. Laps are caused during rolling when overlapping metal does not fuse to the base material.

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Lapping

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Lamination

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Laminations

Plate Lamination4/23/2007 174 of 691

Welding InspectorCodes & Standards Section 7

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Codes & StandardsThe 3 agencies generally identified in a code or standard: The customer, or client The manufacturer, or contractor The 3rd party inspection, or clients representative

Codes often do not contain all relevant data, but may refer to other standards

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Standard/Codes/SpecificationsSTANDARDS

SPECIFICATIONS Examples plate, pipe forgings, castings valves electrodes

CODES Examples pressure vessels bridges pipelines tanks177 of 691

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Welding InspectorWelding Symbols Section 8

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Weld symbols on drawingsAdvantages of symbolic representation: simple and quick plotting on the drawing does not over-burden the drawing no need for additional view gives all necessary indications regarding the specific joint to be obtained

Disadvantages of symbolic representation: used only for usual joints requires training for properly understanding of symbols4/23/2007 179 of 691

Weld symbols on drawingsThe symbolic representation includes: an arrow line a reference line an elementary symbol

The elementary symbol may be completed by: a supplementary symbol a means of showing dimensions some complementary indications4/23/2007 180 of 691

DimensionsConvention of dimensionsIn most standards the cross sectional dimensions are given to the left side of the symbol, and all linear dimensions are give on the right side

BS EN ISO 22553a = Design throat thickness s = Depth of Penetration, Throat thickness z = Leg length (min material thickness)

AWS A2.4In a fillet weld, the size of the weld is the leg length In a butt weld, the size of the weld is based on the depth of the joint preparation

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Weld symbols on drawingsA method of transferring information from the design office to the workshop is:Please weld here

The above information does not tell us much about the wishes of the designer. We obviously need some sort of code which would be understood by everyone. Most countries have their own standards for symbols. Some of them are AWS A2.4 & BS EN 22553 (ISO 2553)

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Weld symbols on drawingsJoints in drawings may be indicated: by detailed sketches, showing every dimension

by symbolic representation

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Elementary Welding Symbols(BS EN ISO 22553 & AWS A2.4)

Convention of the elementary symbols:Various categories of joints are characterised by an elementary symbol. The vertical line in the symbols for a fillet weld, single/double bevel butts and a J-butt welds must always be on the left side.

Weld typeSquare edge butt weldSingle-v butt weld

Sketch

Symbol

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Elementary Welding SymbolsWeld typeSingle-V butt weld with broad root face Single bevel butt weld Single bevel butt weld with broad root face Backing run4/23/2007 185 of 691

Sketch

Symbol

Elementary Welding SymbolsWeld typeSingle-U butt weld Single-J butt weld Surfacing

Sketch

Symbol

Fillet weld4/23/2007 186 of 691

ISO 2553 / BS EN 22553

Plug weld

Square Butt weld

Resistance spot weld

Steep flanked Single-V Butt

Resistance seam weld4/23/2007

Surfacing187 of 691

Arrow Line(BS EN ISO 22553 & AWS A2.4): Convention of the arrow line: Shall touch the joint intersection Shall not be parallel to the drawing Shall point towards a single plate preparation (when only one plate has preparation)

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Reference Line(AWS A2.4) Convention of the reference line:Shall touch the arrow line Shall be parallel to the bottom of the drawing

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Reference Line(BS EN ISO 22553) Convention of the reference line: Shall touch the arrow line Shall be parallel to the bottom of the drawing There shall be a further broken identification line above or beneath the reference line (Not necessary where the weld is symmetrical!)

or

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Double side weld symbols(BS EN ISO 22553 & AWS A2.4) Convention of the double side weld symbols:Representation of welds done from both sides of the joint intersection, touched by the arrow head

Fillet weld

Double bevel

Double J

Double V

Double U

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ISO 2553 / BS EN 22553Reference linesArrow line

Other side

Arrow side

Arrow side

Other side

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ISO 2553 / BS EN 22553MR M

Single-V Butt with permanent backing strip

Single-U Butt with removable backing strip

Single-V Butt flush cap4/23/2007

Single-U Butt with sealing run193 of 691

ISO 2553 / BS EN 22553

Single-bevel butt

Double-bevel butt

Single-bevel butt4/23/2007

Single-J butt194 of 691

ISO 2553 / BS EN 22553s10

10

15

Partial penetration single-V butt S indicates the depth of penetration4/23/2007 195 of 691

ISO 2553 / BS EN 22553a = Design throat thickness s = Depth of Penetration, Throat thickness z = Leg length(min material thickness) a = (0.7 x z)

z

a s

a44mm Design throat

z66mm leg4/23/2007

s66mm Actual throat196 of 691

ISO 2553 / BS EN 22553

Arrow side

Arrow side

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ISO 2553 / BS EN 22553s6

6mm fillet weld

Other side

s6

Other side

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ISO 2553 / BS EN 22553n = number of weld elements l = length of each weld element (e) = distance between each weld element

n x l (e)Welds to be staggered

2 x 40 (50) 3 x 40 (50)

111Process

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ISO 2553 / BS EN 22553All dimensions in mmz5 z65 5

3 x 80 (90)3 x 80 (90)

80

80

80

6 6

90

90

90

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ISO 2553 / BS EN 22553All dimensions in mmz8 3 x 80 (90) 3 x 80 (90)80

z66 6 8 8 90 80 80

90

90

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Supplementary symbols(BS EN ISO 22553 & AWS A2.4)

Convention of supplementary symbolsSupplementary information such as welding process, weld profile, NDT and any special instructions

Site Weld

Toes to be ground smoothly (BS EN only)

Concave or Convex Weld all round

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Supplementary symbols(BS EN ISO 22553 & AWS A2.4) Convention of supplementary symbolsSupplementary information such as welding process, weld profile, NDT and any special instructionsGround flush

MRRemovable backing strip

MPermanent backing strip

111Welding process numerical BS EN

Further supplementary information, such as WPS number, or NDT may be placed in the fish tail4/23/2007 203 of 691

ISO 2553 / BS EN 22553a

b

c4/23/2007

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ISO 2553 / BS EN 22553

Mitre

Convex

Concave

Toes shall be blended205 of 691

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ISO 2553 / BS EN 22553a = Design throat thickness s = Depth of Penetration, Throat thickness z = Leg length(min material thickness) a = (0.7 x z)

z

a s

a44mm Design throat

z66mm leg4/23/2007

s66mm Actual throat206 of 691

ISO 2553 / BS EN 22553 Complimentary Symbols

Field weld (site weld)

Welding to be carried out all round component (peripheral weld)

NDT The component requires NDT inspection

WPS Additional information, the reference document is included in the box207 of 691

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ISO 2553 / BS EN 22553Numerical Values for Welding Processes:111: 121: 131: 135: 136: 141: 311: 72: 15:4/23/2007

MMA welding with covered electrode Sub-arc welding with wire electrode MIG welding with inert gas shield MAG welding with non-inert gas shield Flux core arc welding TIG welding Oxy-acetylene welding Electro-slag welding Plasma arc welding208 of 691

AWS A2.4 Welding Symbols

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AWS Welding Symbols

Depth of Bevel 1(1-1/8) 1/8 60o

Root Opening

Effective Throat

Groove Angle

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AWS Welding SymbolsWelding Process

GSFCAW 1(1-1/8) 1/8 60o

GMAW

GTAWSAW

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AWS Welding SymbolsWelds to be staggered

3 10 3 103SMAW Process

3

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AWS Welding SymbolsSequence of Operations 3rd Operation2nd Operation

1st Operation1(1-1/8) 1/8 60o

FCAW

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AWS Welding SymbolsSequence of Operations RT MT MT1(1-1/8)

FCAW1/8 60o

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AWS Welding SymbolsDimensions- Leg Length

6 leg on member A 6/8

Member A

6 8

Member B4/23/2007 215 of 691

Welding InspectorIntro To Welding Processes Section 9

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Welding ProcessesWelding is regarded as a joining process in which the work pieces are in atomic contact

Pressure welding Forge welding Friction welding

Fusion welding Oxy-acetylene MMA (SMAW)

Resistance Welding

MIG/MAG (GMAW) TIG (GTAW) Sub-arc (SAW) Electro-slag (ESW) Laser Beam (LBW) Electron-Beam (EBW)

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Constant Current Power Source (Drooping Characteristic)100 90 80 70

O.C.V. Striking voltage (typical) for arc initiation Required for: MMA, TIG, Plasma arc and SAW > 1000 AMPS

Voltage

60 50

4030 20

Normal Operating Voltage Range

Large voltage variation, e.g. + 10v (due to changes in arc length)

10 204/23/2007

Small amperage change resulting in virtually constant current e.g. + 5A.40 60 80 100 120 130 140 160 180 200225 of 691

Amperage

Monitoring Heat Input Heat Input: The amount of heat generated in the welding arc per unit length of weld. Expressed in kilo Joules per millimetre length of weld (kJ/mm).

Heat Input (kJ/mm)= Volts x Amps Travel speed(mm/s) x 10004/23/2007 227 of 691

Monitoring Heat Input

Weld and weld pool temperatures

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Monitoring Heat Input

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Monitoring Heat Input Monitoring Heat Input As Required by BS EN ISO 15614-1:2004 In accordance with EN 1011-1:1998When impact requirements and/or hardness requirements are specified, impact test shall be taken from the weld in the highest heat input position and hardness tests shall be taken from the weld in the lowest heat input position in order to qualify for all positions

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Welding InspectorMMA Welding Section 10

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MMA - Principle of operation

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MMA weldingMain features: Shielding provided by decomposition of flux covering Electrode consumable Manual process

Welder controls: Arc length Angle of electrode Speed of travel Amperage settings234 of 691

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Manual Metal Arc Basic Equipment

Control panel (amps, volts) Electrode oven Electrodes Return lead

Power source Holding oven Inverter power source Electrode holder

Welding visor filter glass

Power cables

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MMA Welding PlantTransformer: Changes mains supply voltage to a voltage suitable for welding. Has no moving parts and is often termed static plant. Rectifier: Changes a.c. to d.c., can be mechanically or statically achieved. Generator: Produces welding current. The generator consists of an armature rotating in a magnetic field, the armature must be rotated at a constant speed either by a motor unit or, in the absence of electrical power, by an internal combustion engine. Inverter: An inverter changes d.c. to a.c. at a higher frequency.

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MMA Welding VariablesVoltage The arc voltage in the MMA process is measured as close to the arc as possible. It is variable with a change in arc length O.C.V. The open circuit voltage is the voltage required to initiate, or re-ignite the electrical arc and will change with the type of electrode being used e.g 70-90 volts Current The current used will be determined by the choice of electrode, electrode diameter and material type and thickness. Current has the most effect on penetration. Polarity Polarity is generally determined by operation and electrode type e.g DC +ve, DC ve or AC4/23/2007 237 of 691

Constant Current Power Source (Drooping Characteristic)10090 80 70

O.C.V. Striking voltage (typical) for arc initiation

Voltage

60 50 40 30 20 10 20 40 60 80 100 120 130 140 160 180

Normal Operating Voltage Range

Large voltage variation, e.g. + 10v (due to changes in arc length) Small amperage change resulting in virtually constant current e.g. + 5A.200 239 of 691

Amperage4/23/2007

MMA welding parametersTravel speedToo low wide weld bead contour lack of penetration burn-through Travel speed Too high lack of root fusion incomplete root penetration undercut poor bead profile, difficult slag removal

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MMA welding parametersType of current: voltage drop in welding cables is lower with AC inductive looses can appear with AC if cables are coiled cheaper power source for AC no problems with arc blow with AC DC provides a more stable and easy to strike arc, especially with low current, better positional weld, thin sheet applications welding with a short arc length (low arc voltage) is easier with DC, better mechanical properties DC provides a smoother metal transfer, less spatter

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MMA welding parametersWelding current approx. 35 A/mm of diameter governed by thickness, type of joint and welding

positionToo low poor starting slag inclusions weld bead contour too high lack of fusion/penetration4/23/2007

Welding current

Too high spatter excess penetration undercut burn-through

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MMA welding parametersArc length = arc voltageToo low arc can be extinguished stubbing Arc voltage Too high spatter porosity excess penetration undercut burn-through

Polarity: DCEP generally gives deeper penetration4/23/2007 243 of 691

MMA - Troubleshooting

MMA quality (left to right)current, arc length and travel speed normal; current too low; current too high; arc length too short; arc length too long; travel speed too slow; travel speed too high

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MMA electrode holder

Collet or twist type4/23/2007

Tongs type with spring-loaded jaws245 of 691

MMA Welding Consumables MMA Covered ElectrodesThe three main electrode covering types used in MMA welding

Cellulosic - deep penetration/fusion Rutile - general purpose Basic - low hydrogen(Covered in more detail in Section 14)

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MMA welding typical defectsMost welding defects in MMA are caused by a lack of welder skill (not an easily controlled process), the incorrect settings of the equipment, or the incorrect use, and treatment of electrodes Typical Welding Defects: Slag inclusions Arc strikes Porosity Undercut Shape defects (overlap, excessive root penetration, etc.)

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Manual Metal Arc Welding (MMA)Advantages: Field or shop use Range of consumables All positions Portable Simple equipment High welder skill required High levels of fume Hydrogen control (flux) Stop/start problems Comparatively uneconomic when compared with some other processes i.e MAG, SAW and FCAW

Disadvantages:

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Welding InspectorTIG Welding Section 11

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Tungsten Inert Gas WeldingThe TIG welding process was first developed in the USA during the 2nd world war for the welding of aluminum alloys The process uses a non-consumable tungsten electrode The process requires a high level of welder skill The process produces very high quality welds. The TIG process is considered as a slow process compared to other arc welding processes The arc may be initiated by a high frequency to avoid scratch starting, which could cause contamination of the tungsten and weld

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TIG - Principle of operation

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TIG Welding VariablesVoltageThe voltage of the TIG welding process is variable only by the type of gas being used, and changes in the arc length

CurrentThe current is adjusted proportionally to the tungsten electrodes diameter being used. The higher the current the deeper the penetration and fusion

PolarityThe polarity used for steels is always DC ve as most of the heat is concentrated at the +ve pole, this is required to keep the tungsten electrode at the cool end of the arc. When welding aluminium and its alloys AC current is used4/23/2007 254 of 691

Types of currentDC can be DCEN or DCEP DCEN gives deep penetration can be sine or square wave requires a HF current (continuos or periodical) provide cleaning action

AC Type of welding current

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Pulsed requires special power source current low frequency - up to 20 pulses/sec (thermal pulsing) better weld pool control weld pool partially solidifies 256 of 691 between pulses

Choosing the proper electrodeCurrent type influence

+ + + + +

+

+

+ +

-

Current type & polarity Heat balance Penetration Oxide cleaning action Electrode capacity4/23/2007

DCEN 70% at work 30% at electrode Deep, narrow No Excellent (e.g. 3,2 mm/400A)

AC (balanced) 50% at work 50% at electrode Medium Yes - every half cycle Good (e.g. 3,2 mm/225A)

DCEP 35% at work 65% at electrode Shallow, wide Yes Poor (e.g. 6,4 mm/120A)257 of 691

ARC CHARACTERISTICSConstant Current/Amperage CharacteristicLarge change in voltage = Smaller change in amperageOCV

VoltsLarge arc gap Welding Voltage Small arc gap

Amps4/23/2007 258 of 691

TIG - arc initiation methodsArc initiation method Lift arc simple method tungsten electrode is in contact with the workpiece! high initial arc current due to the short circuit impractical to set arc length in advance electrode should tap the workpiece - no scratch! ineffective in case of AC used when a high quality is not essential4/23/2007

HF startneed a HF generator (sparkgap oscillator) that generates a high voltage AC output (radio frequency) costly reliable method required on both DC (for start) and AC (to re-ignite the arc) can be used remotely HF produce interference requires superior insulation259 of 691

Pulsed current usually peak current is 2-10 times Pulse Cycle Peak Background background current time time current current useful on metals sensitive to high heat input reduced distortions in case of dissimilar thicknesses equal penetration can be achievedCurrent (A)

Average current Time

one set of variables can be used in all positions used for bridging gaps in open root joints require special power source4/23/2007 260 of 691

Choosing the proper electrodePolarity Influence cathodic cleaning effect

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Tungsten ElectrodesOld types: (Slightly Radioactive) Thoriated: DC electrode -ve - steels and most metals 1% thoriated + tungsten for higher current values 2% thoriated for lower current values Zirconiated: AC - aluminum alloys and magnesium

New types: (Not Radioactive) Cerium: DC electrode -ve - steels and most metals Lanthanum: AC - Aluminum alloys and magnesium

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TIG torch set-up Electrode extension

StickoutElectrode extension

2-3 times electrode diameter

Low electron emission Unstable arc4/23/2007

Too small

Electrode extension

Too large

Overheating Tungsten inclusions263 of 691

Choosing the correct electrodePolarity Influence cathodic cleaning effect

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Tungsten ElectrodesOld types: (Slightly Radioactive) Thoriated: DC electrode -ve - steels and most metals 1% thoriated + tungsten for higher current values 2% thoriated for lower current values Zirconiated: AC - aluminum alloys and magnesium

New types: (Not Radioactive) Cerium: DC electrode -ve - steels and most metals Lanthanum: AC - Aluminum alloys and magnesium

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Tungsten electrode typesPure tungsten electrodes:colour code - green no alloy additions low current carrying capacity maintains a clean balled end can be used for AC welding of Al and Mg alloys poor arc initiation and arc stability with AC compared with other electrode types used on less critical applications low cost4/23/2007 266 of 691

Tungsten electrode typesThoriated tungsten electrodes:colour code - yellow/red/violet

20% higher current carrying capacity compared to pure tungsten electrodeslonger life - greater resistance to contamination

thermionic - easy arc initiation, more stable arcmaintain a sharpened tip

recommended for DCEN, seldom used on AC (difficult to maintain a balled tip)This slightly radioactive4/23/2007 267 of 691

Tungsten electrode typesCeriated tungsten electrodes:colour code - grey (orange acc. AWS A-5.12)

operate successfully with AC or DCCe not radioactive - replacement for thoriated types

Lanthaniated tungsten electrodes:colour code - black/gold/blue

operating characteristics similar with ceriated electrode

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Tungsten electrode typesZirconiated tungsten electrodes:colour code - brown/white

operating characteristics fall between those of pure and thoriated electrodesretains a balled end during welding - good for AC welding high resistance to contamination preferred for radiographic quality welds

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Electrode tip for DCENPenetration increase2-2,5 times electrode diameter

IncreaseVertex angle

Decrease Bead width increaseElectrode tip prepared for low current welding4/23/2007

Electrode tip prepared for high current welding270 of 691

Electrode tip for ACDC -ve AC

Electrode tip ground4/23/2007

Electrode tip ground and then conditioned271 of 691

TIG Welding VariablesTungsten electrodesThe electrode diameter, type and vertex angle are all critical factors considered as essential variables. The vertex angle is as shown

DC -ve

AC

Vetex angle Note: too fine an angle will promote melting of the electrodes tip4/23/2007

Note: when welding aluminium with AC current, the tungsten end is chamfered and forms a ball end when welding272 of 691

Choosing the proper electrodeFactors to be considered: Electrode tip not properly heated Excessive melting or volatilisation

Too low

Welding current

Too high

Unstable arc

Penetration

Tungsten inclusions

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Shielding gas requirements Preflow and postflowShielding gas flow Welding current

Preflow

Postflow

Flow rate too low

Flow rate too high

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Special shielding methodsPipe root run shielding Back Purging to prevent excessive oxidation during welding, normally argon.

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TIG torch set-upElectrode extension

StickoutElectrode extension

2-3 times electrode diameter

Low electron emission Unstable arc4/23/2007

Too small

Electrode extension

Too large

Overheating Tungsten inclusions277 of 691

TIG Welding ConsumablesWelding consumables for TIG: Filler wires, Shielding gases, tungsten electrodes (nonconsumable). Filler wires of different materials composition and variable diameters available in standard lengths, with applicable code stamped for identification Steel Filler wires of very high quality, with copper coating to resist corrosion. shielding gases mainly Argon and Helium, usually of highest purity (99.9%).

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Tungsten InclusionMay be caused by Thermal Shock of heating to fast and small fragments break off and enter the weld pool, so a slope up device is normally fitted to prevent this could be caused by touch down also.Most TIG sets these days have slopeup devices that brings the current to the set level over a short period of time so the tungsten is heated more slowly and gently

A Tungsten Inclusion always shows up as bright white on a radiograph4/23/2007 279 of 691

TIG typical defectsMost welding defects with TIG are caused by a lack of welder skill, or incorrect setting of the equipment. i.e. current, torch manipulation, welding speed, gas flow rate, etc.

Tungsten inclusions (low skill or wrong vertex angle) Surface porosity (loss of gas shield mainly on site) Crater pipes (bad weld finish technique i.e. slope out)

Oxidation of S/S weld bead, or root by poor gas cover Root concavity (excess purge pressure in pipe) Lack of penetration/fusion (widely on root runs)

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Tungsten Inert Gas WeldingAdvantages High quality

Disadvantages High skill factor required

Good control All positions Lowest H2 process Minimal cleaning Autogenous welding

Low deposition rate Small consumable range High protection required Complex equipment Low productivity

(No filler material) Can be automated4/23/2007

High ozone levels +HF

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Welding InspectorMIG/MAG Welding Section 12

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Gas Metal Arc WeldingThe MIG/MAG welding process was initially developed in the USA in the late 1940s for the welding of aluminum alloys. The latest EN Welding Standards now refer the process by the American term GMAW (Gas Metal Arc Welding) The process uses a continuously fed wire electrode The weld pool is protected by a separately supplied shielding gas The process is classified as a semi-automatic welding process but may be fully automated The wire electrode can be either bare/solid wire or flux cored hollow wire

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MIG/MAG - Principle of operation

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MIG/MAG process variables Welding currentIncreasing welding current Increase in depth and width Increase in deposition rate

Polarity

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MIG/MAG process variables Arc voltage

Increasing arc voltage Reduced penetration, increased width Excessive voltage can cause porosity, spatter and undercut

Travel speedIncreasing travel speed Reduced penetration and width, undercut4/23/2007 287 of 691

Gas Metal Arc WeldingTypes of Shielding Gas MIG (Metal Inert Gas) Inert Gas is required for all non-ferrous alloys (Al, Cu, Ni) Most common inert gas is Argon Argon + Helium used to give a hotter arc - better for thicker joints and alloys with higher thermal conductivity

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MIG/MAG shielding gasesType of material Shielding gasCO2 , Ar+(5-20)%CO2

Carbon steel

Stainless steel

Ar+2%O2

Aluminium

Ar

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MIG/MAG shielding gasesAr Ar-He He CO2

Argon (Ar): higher density than air; low thermal conductivity the arc has a high energy inner cone; good wetting at the toes; low ionisation potential Helium (He): lower density than air; high thermal conductivity uniformly distributed arc energy; parabolic profile; high ionisation potential Carbon Dioxide (CO2): cheap; deep penetration profile; cannot support spray transfer; poor wetting; high spatter4/23/2007 291 of 691

MIG/MAG shielding gasesGases for dip transfer: CO2: carbon steels only: deep penetration; fast welding speed; high spatter levels Ar + up to 25% CO2: carbon and low alloy steels: minimum spatter; good wetting and bead contour 90% He + 7.5% Ar + 2.5% CO2:stainless steels: minimises undercut; small HAZ Ar: Al, Mg, Cu, Ni and their alloys on thin sections

Ar + He mixtures: Al, Mg, Cu, Ni and their alloys on thicker sections (over 3 mm)4/23/2007 292 of 691

MIG/MAG shielding gasesGases for spray transfer Ar + (5-18)% CO2: carbon steels: minimum spatter; good wetting and bead contour Ar + 2% O2: low alloy steels: minimise undercut; provides good toughness Ar + 2% O2 or CO2: stainless steels: improved arc stability; provides good fusion Ar: Al, Mg, Cu, Ni, Ti and their alloys Ar + He mixtures: Al, Cu, Ni and their alloys: hotter arc than pure Ar to offset heat dissipation Ar + (25-30)% N2: Cu alloys: greater heat input4/23/2007 293 of 691

Gas Metal Arc WeldingTypes of Shielding Gas MAG (Metal Active Gas) Active gases used are Oxygen and Carbon Dioxide Argon with a small % of active gas is required for all steels (including stainless steels) to ensure a stable arc & good droplet wetting into the weld pool Typical active gases are Ar + 20% CO2 for C-Mn & low alloy steels Ar + 2% O2 100% CO24/23/2007

for stainless steels can be used for C - steels294 of 691

MIG/MAG Gas Metal Arc WeldingElectrode orientation

PenetrationUndercut

Deep

Moderate Shallow

Excess weld metal Maximum Moderate Minimum Severe Moderate Minimum

Electrode extension4/23/2007

Increased extension

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MIG / MAG - self-regulating arcStable conditionArc length L = 6,4 mm Arc voltage = 24V Welding current = 250A WFS = 6,4 m/min Melt off rate = 6,4 m/min

Sudden change in gun positionArc length L = 12,7 mm Arc voltage = 29V Welding current = 220A WFS = 6,4 m/min Melt off rate = 5,6 m/min

L

19 mm

L

25 mm

Voltage (V)

Current (A)4/23/2007 296 of 691

MIG/MAG - self-regulating arcSudden change in gun positionArc length L = 12,7 mm Arc voltage = 29V Welding current = 220A WFS = 6,4 m/min Melt off rate = 5,6 m/min

Re-established stable conditionArc length L = 6,4 mm Arc voltage = 24V Welding current = 250A WFS = 6,4 m/min Melt off rate = 6,4 m/min

L

25 mm L

25 mm

Voltage (V)

Current (A)4/23/2007 297 of 691

Terminating the arcCrater fill Burnback time delayed current cut-off to prevent wire freeze in the weld end crater depends on WFS (set as short as possible!)Contact tip3 mm 8 mm 14 mm Insulatin g slag Burnback time 0.05 sec Workpiec e4/23/2007

Current - 250A Voltage - 27V WFS - 7,8 m/min Wire diam. - 1,2 mm Shielding gas Ar+18%CO2298 of 691

0.10 sec

0.15 sec

MIG/MAG - metal transfer modes

Contact tip extension (0-3,2 mm)

Electrode extension 6-13 mm

Contact tip recessed (3-5 mm)

Electrode extension 19-25 mm

Set-up for dip transfer4/23/2007

Set-up for spray transfer299 of 691

MIG/MAG - metal transfer modesVoltageElectrode diameter = 1,2 mm WFS = 8,3 m/min

Current = 295 AVoltage = 28V

Globular transfer

Spray transferElectrode diameter = 1,2 mm WFS = 3,2 m/min Current = 145 A

Dip transfer

Voltage = 18-20V

Current

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Current/voltage conditions

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MIG/MAG-methods of metal transferDip transferTransfer occur due to short circuits between wire and weld pool, high level of spatter, need inductance control to limit current raise

Can use pure CO2 or Ar- CO2 mixtures as shielding gasMetal transfer occur when arc is extinguished

Requires low welding current/arc voltage, a low heat input process. Resulting in low residual stress and distortion Used for thin materials and all position welds4/23/2007 303 of 691

MIG/MAG-methods of metal transferSpray transferTransfer occur due to pinch effect NO contact between wire and weld pool! Requires argon-rich shielding gas Metal transfer occur in small droplets, a large volume weld pool Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion Used for thick materials and flat/horizontal position welds4/23/2007 306 of 691

MIG/MAG-methods of metal transferPulsed transfer Controlled metal transfer, one droplet per pulse, No transfer between droplet and weld pool! Requires special power sources

Metal transfer occur in small droplets (diameter equal to that of electrode)Requires moderate welding current/arc voltage, a reduced heat input . Resulting in smaller residual stress and distortion compared to spray transfer Pulse frequency controls the volume of weld pool, used for root runs and out of position welds4/23/2007 307 of 691

MIG/MAG - metal transfer modesPulsed transferControlled metal transfer. one droplet per pulse. NO transfer during background current! Requires special power sources Metal transfer occur in small droplets (diameter equal to that of electrode) Requires moderate welding current/arc voltage, reduced heat input smaller residual stress and distortions compared to spray transfer Pulse frequency controls the volume of weld pool, used for root runs and out of position welds4/23/2007 308 of 691

MIG/MAG-methods of metal transferGlobular transferTransfer occur due to gravity or short circuits between drops and weld pool Requires CO2 shielding gas Metal transfer occur in large drops (diameter larger than that of electrode) hence severe spatter Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion Non desired mode of transfer!

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Flat or Constant Voltage CharacteristicFlat or Constant Voltage Characteristic Used With MIG/MAG, ESW & SAW < 1000 ampsO.C.V. Arc Voltage Virtually no Change.

33 32 31

Voltage

Small Voltage Change. Large Current Change

100

Amperage

200

300

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MIG/MAG welding gun assemblyContact tip Gas diffuser The Push-Pull gun

Union nut

Gas nozzle

Trigger

Handle4/23/2007

WFS remote control potentiometer

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Gas Metal Arc WeldingPROCESS CHARACTERISTICS

Requires a constant voltage power source, gas supply, wire feeder, welding torch/gun and hose package Wire is fed continuously through the conduit and is burnt-off at a rate that maintains a constant arc length/arc voltage Wire feed speed is directly related to burn-off rate Wire burn-off rate is directly related to current When the welder holds the welding gun the process is said to be a semi-automatic process The process can be mechanised and also automated In Europe the process is usually called MIG or MAG4/23/2007 318 of 691

MIG/MAG typical defectsMost welding imperfections in MIG/MAG are caused by lack of welder skill, or incorrect settings of the equipment Worn contact tips will cause poor power pick up, or transfer

Bad power connections will cause a loss of voltage in the arcSilica inclusions (in Fe steels) due to poor inter-run cleaning Lack of fusion (primarily with dip transfer)

Porosity (from loss of gas shield on site etc)Solidification problems (cracking, centerline pipes, crater pipes) especially on deep narrow welds

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WELDING PROCESSFlux Core Arc Welding (Not In The Training Manual)

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Flux cored arc weldingFCAW methods

With gas shielding Outershield

Without gas shielding Innershield

With metal powder Metal core

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Outershield - principle of operation

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Innershield - principle of operation

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ARC CHARACTERISTICSConstant Voltage Characteristic

OCVLarge arc gap Small arc gap

Small change in voltage = large change in amperage

Volts

The self adjusting arc.

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Flux Core Arc Welding (FCAW)Flux core Insulated extension nozzle

Current carrying guild tubeWire joint Flux cored hollow wire

Flux powderArc shield composed of vaporized and slag forming compounds

Flux core wires

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Solidified weld metal and slag

Molten weld pool

Metal droplets covered with thin slag coating328 of 691

Flux cored arc weldingFCAW methods

With gas shielding Outershield

Without gas shielding Innershield (114)

With metal powder Metal core

With active gas shielding (136)4/23/2007

With inert gas shielding (137)329 of 691

FCAW - differences from MIG/MAG usually operates in DCEP but some Innershield wires operates in DCEN power sources need to be more powerful due to the higher currents doesn't work in deep transfer mode require knurled feed rolls Innershield wires use a different type of welding gun4/23/2007 330 of 691

Backhand (drag) techniqueAdvantagespreferred method for flat or horizontal position slower progression of the weld deeper penetration weld stays hot longer, easy to remove dissolved gasses

Disadvantagesproduce a higher weld profile difficult to follow the weld joint can lead to burn-through on thin sheet plates4/23/2007 331 of 691

Forehand (push) techniqueAdvantagespreferred method for vertical up or overhead position arc is directed towards the unwelded joint , preheat effect easy to follow the weld joint and control the penetration

Disadvantagesproduce a low weld profile, with coarser ripples fast weld progression, shallower depth of penetration the amount of spatter can increase

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FCAW advantages less sensitive to lack of fusion requires smaller included angle compared to MMA high productivity all positional smooth bead surface, less danger of undercut basic types produce excellent toughness properties good control of the weld pool in positional welding especially with rutile wires seamless wires have no torsional strain, twist free ease of varying the alloying constituents no need for shielding gas4/23/2007 333 of 691

FCAW disadvantages limited to steels and Ni-base alloys slag covering must be removed FCAW wire is more expensive on a weight basis than solid wires (exception: some high alloy steels) for gas shielded process, the gaseous shield may be affected by winds and drafts more smoke and fumes are generated compared with MIG/MAG in case of Innershield wires, it might be necessary to break the wire for restart (due to the high amount of insulating slag formed at the tip of the wire)

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FCAW advantages/disadvantagesAdvantages: Disadvantages:

1) Field or shop use2) High productivity 3) All positional 4) Slag supports and shapes the weld Bead

1) High skill factor2) Slag inclusions 3) Cored wire is Expensive 4) High level of fume (Inner-shield) 5) Limited to steels and nickel alloys335 of 691

5) No need for shielding gas

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Welding InspectorSubmerged Arc Welding Section 13

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Submerged Arc Welding Introduction Submerged arc welding was developed in the Soviet Union during the 2nd world war for the welding of thick section steel. The process is normally mechanized. The process uses amps in the range of 100 to over 2000, which gives a very high current density in the wire producing deep penetration and high dilution welds. A flux is supplied separately via a flux hopper in the form of either fused or agglomerated. The arc is not visible as it is submerged beneath the flux layer and no eye protection is required.

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SAW Principle of operation

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Principles of operationFactors that determine whether to use SAW chemical composition and mechanical properties required for the weld deposit thickness of base metal to be welded joint accessibility position in which the weld is to be made frequency or volume of welding to be performed

SAW methods

Semiautomatic4/23/2007

Mechanised

Auto